DESCRIPTION: (Adapted from abstract.) This project is focused on the investigation of molecular mechanisms of myotonic dystrophy (DM), a disease characterized by weakness and myotonia of skeletal muscle, impaired systolic contraction of cardiac muscle, and cardiomyopathy, together with cataracts, mental retardation and endocrine abnormalities. Mutations for DM is an expanded CTG triplet repeat located in the 3' untranslated region of the myotonin protein kinase (Mt-PK) gene. The molecular mechanism of the pathogenesis of DM is unknown. The investigators recently identified a family of novel proteins with binding activities specific for triplet repeats and particular CUG-BP protein specific for RNA CUG repeats. CUG-BP protein was purified from HeLa cells and found to be identical to a novel RNA-binding protein Nab2p, which plays an essential role in the regulation of poly(A) tail length and/or nucleocytoplasmic export of mRNAs. The investigators hypothesize that CUG triplet repeat binding proteins regulate processing and transport of MRNAs containing CUG repeats such as Mt-PK mRNA and that a large increase in the number of CUG triplet repeat impairs processing/transport of these mRNAs and is responsible for the pathogenesis of DM. In the first specific aim, the investigators will examine the potential role of CUG-BP/Nab60 in the regulation of the Mt-PK mRNA processing and transport. Stable clonal cell lines containing over-expressed (CUG)n repeats or over-expressed CUG-BP/Nab50 will be used to determine whether alteration of CUG-BP/Nab50 protein alters the expression of Mt-PK mRNA from the mutant allele of the Mt.-PK gene. In Specific Aim 2, they propose to search for other MRNAs that are regulated by CUG-BP/Nab50. In specific Aim 3, CUG-BP/Nab50 RNA and protein levels and its CUG binding activity will be determine in cultured cells and tissues derived from normal controls, DM patients, and Mt-PK knock-out mice. In Specific Aim 4, the propose to knock out the CUG-BP/Nab50 gene in a mouse and determine the biochemical, physical and morphological phenotypic manifestations. If the hypotheses are correct, one would expect to see some features similar to the DM phenotype. Results of these experiments provide insight into the function of this newly identified family of proteins and determine their role in pathogenesis. of DM.